Control system for welding inspection machine

ABSTRACT

This patent discloses a crawler for moving through a pipeline and emitting rays at the location of circumferential welds in the pipeline to expose film positioned about the exterior of the pipe to check the weld. Movement of the crawler and control of the emission of the rays is provided by control circuitry responsive to a signal received from exterior of the pipeline.

United States Patent Ketchbaw et al.

[ 1 Sept. 12, 1972 CONTROL SYSTEM FOR WELDING INSPECTION MACHINE [72]inventors: Thomas E. Ketchbaw; Robert D. Foster; Kiryako Arvanetakis,all of Houston, Tex.

[73] Assignee: Houston Gamma Ray Company,

Houston, Tex.

[22] Filed: June 6, 1968 [21] Appl. No.: 735,061

[52] US. Cl ..250/91, 250/65 R, 250/83.3 D [51] Int. Cl. ..G03b 41/16,GOlt 1/16 [58] Field of Search.....250/65 F, 93, 43.5 D, 43.5 R,

[56] References Cited UNITED STATES PATENTS 3,492,477 Arnesen ..250/652,532,536 12/1950 Boucher ..250/65 3,087,058 4/1963 Arvanetakis et al.....250/65 X 3,272,987 9/1966 Kohn et al. ..250/ 106 3,316,406 4/1967Sauerwein et al. ..250/106 Primary Examiner-James W. Lawrence AssistantExaminer-Davis L. Willis Attorney-J. Vincent Martin, Joe E. Edwards andM. H. Gay

[57] ABSTRACT This patent discloses a crawler for moving through apipeline and emitting rays at the location of circumferential welds inthe pipeline to expose film positioned about the exterior of the pipe tocheck the weld. Movement of the crawler and control of the emission ofthe rays is provided by control circuitry responsive to a signalreceived from exterior of the pipeline.

13 Claims, 10 Drawing Figures PATENTEDSEP 12 I972 SHEET 6 0F 7 v W -HH+-ram mm CONTROL SYSTEM'FOR WELDING INSPECTION MACHINE This inventionrelates to checking of circumferential welds in a pipeline, andparticularly relates to a crawler for moving through a pipeline andexposing film wrapped around the pipeline at selected circumferentialwelds.

In the past weld inspection machines utilizing X-ray tubes have been runinside of a pipeline. Movement of the machine, as well as operation ofthe X-ray device, was controlled by cables extending to the end of thepipeline. The length of pipeline which could be inspected was thusrestricted. Also, great difficulty was experienced in locating thecrawler in the pipeline opposite a weld.

In recent years, radio-active source material has been used to exposefilm, but there has been no known device for moving the radio-activesource along the in side of the pipeline. The use of this type of sourcehas been from the exterior of the pipeline in the same manner as X-raymachines have been positioned exteriorly of the pipeline in the past.This is disadvantageous, as with both the X-ray machine and theradio-active source a number of shots are taken to X-ray a completecircumferential weld. Thus, if a machine be available for moving eitheran X-ray tube or radio-active source through a pipeline and exactlypositioning it at a weld without the need for elaborate cables extendingthrough the pipeline to control the machine, then the speed with whichcircumferential welds could be inspected would obviously be greatlyincreased.

It is an object of this invention to provide a weld-inspection crawlerwhich can be controlled from the exterior of a pipeline without directconnections.

Another object is to provide a weld-inspection crawler for moving asource of radio-active material through a pipeline to inspect the welds.

Another object is to provide a weld-inspection crawler which may be madeto move forward or back or stop at selected locations without the use ofcables or the like extending down the pipeline.

Another object is to provide a weld-inspection crawler which may becontrolled in its movement in both directions and caused to stop at aparticular location and generate rays for exposing film by remotecontrol.

Another object is to provide a weld-inspection crawler as above withadequate safety features so that the emission of rays exteriorly of thepipe will be stopped after a selected time in the event of malfunctionof the crawler.

Another object is to provide a simple inexpensive control system for acrawler which will remotely control the movement of the crawler in bothdirections in a pipeline and will control the emission of rays to theexterior of the crawler to inspect a weld utilizing successive signalsto simplify controls.

Another object is to provide a simple inexpensive control system for acrawler which will, by remote control, determine movement of the crawlerthrough the pipeline in either direction, stop the crawler at an exactlocation within the pipe, and control the movement of a radio-activesource out of and return it into a shield to inspect a circumferentialweld in a pipeline.

Other objects, features and advantages will be apparent from thedrawings, the specification and the claims.

In the drawings, wherein an illustrative embodiment of this invention isshown, and wherein like numerals indicate like parts:

FIG. 1 is a birds-eye view of a crawler constructed in accordance withthis invention;

FIG. 2 is a side view in elevation of the crawler shown in FIG. 1;

FIG. 3 is a front view in elevation of the crawler of FIG. 1;

FIG. 4 is a fragmentary view taken along line 4-4 of FIG. 3, partiallyin section, partially in elevation and partially in phantom, showing apipe weld being inspected by a source of radio-active material carriedby the crawler of FIG. 1;

FIG. 5 is a fragmentary view along the lines 5-5 of FIG. 1, illustratingthe power means for extending and retracting the radio-active sourcefrom the camera;

FIG. 6 is a view partially in cross-section and partially in elevation,illustrating the source control motor, its self-locking gear drive, andthe clutch utilized for safety purposes to provide for retraction of thesource in the event of a power loss of malfunction of the system;

FIGS. 7, 8 and 9 are schematic diagrams showing the control system forthe crawler; and

FIG. 10 shows an optional safety circuit which may be employed.

Reference is first made to FIGS. 1 through 6 which illustrate themechanical details of the crawler.

The crawler body 10 is supported on the front by a pair of wheels 11 and12 which will be seen in FIG. 3 to be spaced arcuately approximatelyapart. In the rear the crawler is supported by the wheel 13 whicharcuately bisects the two front wheels 11 and 12. It will be notedparticularly from FIG. 3 that the center of gravity of the machine isvery low and that the machine will be supported on the three wheels ll,12 and 13 in the bottom of the pipe.

Means are provided on the body for moving the crawler through a pipe.Preferable this means includes a pair of drive wheels which are drivenby motor 16 through gears not shown in the gear box 17 and through thechains 18 and 19. The drive wheel 15 is mounted on an arm 21 pivotedabout the rotational axis of sprocket 22 (FIG. 3). In like manner, thedrive wheel 14 is supported on an arm 23 which is pivoted about thecenter of rotation of the sprocket 24. A piston cylinder arrangementindicated generally at 25 extends between the shafts on which the twodrive wheels 14 and 15 are mounted. Compressed air from container 26exerts a force within the cylinder-piston assembly to urge the wheels 14and 15 apart, and thus into firm engagement with the wall of the pipe.As the compressed gas is resilient in nature, the drive wheels will stayfirmly in engagement with the pipe even though the pipe will change inits configuration along its length.

The motor 16 is of the reversing type and may be made to run in eitherdirection to drive the crawler in either direction through a pipe.

Power for the motor 16 is provided by heavy duty l2-volt batteries inthe battery box indicated generally at 27.

A source of rays for exposing film is carried by the body and in thepreferred embodiment a source of radio-active material 28 (FIG. 4) iscarried in the shield indicated generally at 29 when the source is notin use.

Connected to the shield 29 is a spool-like shield 31 into which thesource is projected when film is being exposed.

The shield 29 is conventional in construction and, as shown in thecut-away view, when the source 28 is retracted, the lead shieldingprevents any rays from escaping as the passageway through the shield hastwo 90' bends with the source 28 between the bends when in retractedposition. When the source is extended, it passes through the couplingindicated generally at 32, and the tube 33 which extends from thecoupling into the center of the spool 31.

The spool 31 includes two spaced shield sections 34 and 35. These haveconfronting frusto-conical faces and are made of lead. The centersection 36 is a short tubular piece of aluminum. A plurality of rods 37are positioned circumferentially about the thick aluminum tubing 35 andthe lead shield portion 36 is poured about these rods 37 to attach theshield 35 to the center section 36. A plurality of Allen-head screws 38are spaced circumferentially about and attach the lead shield 34 to thecentral aluminum section 36.

In the use of the crawler, a film in a suitable plastic containerindicated generally at 39 is wrapped about a weld 41. Through a suitablecontrol system to be explained hereinbelow, a signal sent from thesignal generator 42 is received by the signal receiver 43 and stops thecrawler in the position shown in FIG. 4. Subsequent signals extend thesource 28 to the position shown in FIG. 4 to expose the film in thecarrier 39. Subsequent signal received by the receiver 43 retracts thesource 28 to its position shown in the camera 29.

As shown in FIGS. 1 and 4, the source is extended and retracted by acable 20 to which the source is attached. The cable 20 reciprocateswithin the flexible tube 30. Means are provided to reciprocate the cable20 to move the source between a position within and a position withoutcamera 29.

Referring to FIGS. and 6, it will be seen that the tube 20 at its endremote from the shield is attached to a support 44 and the cable 20 isattached to a rack 45. The means for moving the source into and out ofthe shield 29 includes a reversing motor indicated generally at 46connected through a gear train including the worm 47 and worm gear 48(FIG. 6) and the clutch indicated generally at 49 to the rack 45. Theworm 47 and worm gear 48 provide a self-locking gear train and theclutch 49 provides a means for releasing the rack 45 from theself-locking gear train. When released the source is returned to thecamera by the resilient means provided by spring 51 exerting a force onthe rack through cable 52 which is trained about pulley 53.

Referring to the clutch (FIG. 6) the output from the worm gear 48 istransmitted through gear 54 to the shaft 55. Shaft 55 has a bushing 56thereon and the rack pinion 57 is rotatably mounted on the bushing 56. Afriction clutch member 58 is non-rotatably mounted on the shaft 55 andcooperates with a friction member 59 which is mounted on and keyed tothe shaft portion 57a of the pinion gear 57 through a sleeve 60. Thefriction member 59 is free to move axially within a limited area sothat, upon energizing of the coil 61, the friction members 58 and 59will be drawn together to provide rotation of the rack pinion 57inresponse to rotation of the worm 47. If a malfunction in controlsoccurs, the coil 61 is de-energized, as will be more fully explainedhereinafter, to release the frictional engagement between the members 58and 59, and the spring 51 returns the source into the shield 29.

With the clutch 49 activated, the motor 46 will drive the rack 45 alongits guideway 62 to extend or retract the source. At the limits of itsmovement in each direction, the rack activates micro-switches 40 or 50,depending on the direction of movement, to shut off motor 46, as will bemore fully explained hereinafter.

Reference is now made to FIGS. 7, 8 and 9 which show a control system.

A signal-generating means is provided which includes an electro-magnetsignal generator 42 (FIGS. 4 v

and 7). The electro-magnet is energized by a suitable source of llO-voltcurrent by closing of the switch 63. As previously explained, thiselectro-magnet 42 is placed on the pipe relative to the crawler so thata signal from the electro-magnet will be picked up by the receiving coil43 carried on the crawler. After the crawler has been started, theelectro-magnet is moved to a position in which it is desired to stop thecrawler, and, when the crawler moves to a position where the next signalis picked up by the receiving coil coming into proximity with thesending coil, a second signal will be received which will stop thecrawler as shown in FIG. 4.

It will be appreciated that the electro-magnet will generate a fieldwhich will extend out a foot or two from the electro-magnet inside thepipe. By adjusting the gain on the receiving system, the receiving coil43 will pick up a signal at a selected proximity to the sending coil 42.Preferably the gain is selected so that an operative signal is receivedwhen the pickup coil is immediately below the signal-generating coil asshown in FIG. 4.

The signal received from the pickup coil 43 is amplified in theamplifier A and operates the relay 64 to step the stepping relayindicated generally at 65 one step. Stepping relay 65 is a lockout relaywhich will not step again until after the previous signal has beenreversed. Alternate positions are dead. It will be noted that when therelay 64 is closed, a current from a suitable source indicated generallyat 67 passes through the coil 68 to activate the stepping relay onestep. If it be assumed that at the beginning of operations the steppingswitch 66 was at the one position, no output signal would be present asthe position is dead. Upon the signal generator 42 being brought intoproximity with the receiving coil 43 and the switch 64 closed togenerate a signal, the stepping coil will step to position 2.

Forward motion of the crawler is provided by steppingrelay 65 toposition 2. With the relay in position 2, current flows from the source67 through line 69 to contact 2 of the relay and thence through line 71to the forward relay 72. Upon closing of forward relay 72, current flowsthrough the second forward relay 73 through lines 74, 75 and 76 toactivate the second relay. Line 76 is connected to the negative terminalof the power source 67.

It might be noted that throughout the control system multiple relays areused for convenience and to permit stepping up the current so that onlya small current will pass through the stepping relay 65 to increase itsuseful life.

In FIG. 9 the main power source (l2-volt batteries) is shown at 77, andthe power source 67 of FIG. 7 will be connected to this l2-volt battery.It might be noted that this battery is separate from the battery 78which drives the amplifier A. A separate battery is provided for theamplifier so that a constant power will be available for the amplifier.It will be appreciated that the main battery 77 operates all of thevarious motors and its available power will vary substantially betweencharges.

Upon closing of the second forward relay 73, current flows from thebattery 77 through relay 73, line 78, and line 79 through the closedcontact 81 of the reverse relay 80, and thence to the motor 16. Frommotor 16 current flows through line 82, closed contact 83 of the reverserelay 80 and line 84 to the motor shunt 85 and thence through line 86 tothe battery 77. Thus, with the stepping relay 65 in the number 2position, the crawler motor is operating to drive the crawler in aforward direction through the pipe.

Stopping of the crawler is provided for by moving stepping relay 65 toposition 3. The signal-generating electro-magnet 42 is positionedrelative to a weld 41 as shown in FIG. 4, and the switch 63 closed. Bymoving the electro-magnet away from the pickup coil 43, the relay 64 isde-energized and the stepping relay 65 is now in condition to step tocontact 3 upon receiving the next signal, which it will do when thepickup coil 43 comes into proximity with the sending coil 42. Thisdisconnects the control current to the forward relay 72 and opens thisrelay to stop the motor 16.

The operator then opens the switch 63 to de-energize the sending coiland the stepping relay is now ready to receive a third signal.

Advancing stepping relay to position 4 extends source 28. Upon the thirdsignal being sent by closing of the switch 63, the relay steps toposition 4. Current passes through position 4 and line 87 to the sourcerelay 88. Upon source relay 88 being closed, current flows through lines75 and 89 to a second source relay 90. Current also passessimultaneously through lines 91 and 92 to clutch relay 93. Closing ofthe source relay 90 provides a current through line 100, the forwardlimit switch 40 which is now closed as the source is retracted and inthe shield, through switch contact 94, line 95, to the source motor 46.Current returns to battery through line 95a, contact 96 which is in itsup position and line 97. This activates the source motor in a directionto extend the source.

In the meanwhile, the clutch relay 93 has been activated to shift thecontacts to their up position and current flows from the battery 77through line 98, contact 99, and line 101 to the clutch 49, thencethrough line 103 and the time-delay 104 which is in closed position, tomidpoint of the coil 105 (clutch 49 requires 6 volts) and returns to thebattery through line 106, contact 107 and line 108. Thus, with thesource motor operating and the clutch 49 energized, the rack 45 willmove rearwardly of the crawler until it strikes the forward limit switch40 to open the switch and break the circuit to stop the motor.

Returning the source to the shield results from stepping relay 65 toposition 5. After the film has been exposed, the control switch 63 isopened to take the signal off the relay 64, and then closed again tomove the stepping relay 65 to contact 5. This de-energizes the threerelays 88, and 93, and returns the contacts 94 and 96 of relay 90, and99 and 107 of relay 93 to the position shown in the drawings. In thisposition current flows in the clutch system through lines 98, contact99, line 101, through .clutch 49 to line 103, through the closedtime-delay relay 104, coil 105, line 106, contact 107 and 108 tobattery. Thus, the clutch is still energized.

The reverse limit switch was closed upon the rack 45 moving forward, andnow a current may flow through line 100, the reverse limit switch 50,contact 96 and line to source motor 46, and thence return to the batterythrough line 95, contact 94 and line 97 to operate the motor in thereverse direction to withdraw the source and return it to the camera.

If a malfunction occurs, time-delay 104 becomes operative to de-energizeclutch 49 to permit spring 51 to return the source to the shield. Itwill be noted that when contact 107 is in its down position, currentflows through the contact, the time-delay relay 104, line 109, reverselimit switch 50 and line 100, to the battery 77. Thus, upon the steppingswitch being stepped to position 5, the time-delay 104 is energized. Iffor some reason there is a malfunction in the system and the rack 45does not move into contact with the reverse limit switch 64 to break thecircuit, the time-delay 104 will, after a selected time interval, openthe contact 111 to break the circuit through clutch 49 and de-energizethe clutch 49. If this occurs, the current is taken off the coil 61(FIG. 6) to de-energize the clutch and the spring 51 will mechanicallyreturn the source to the shield.

Reverse movement of the crawler is provided by stepping relay 65 toposition 6. After the source has been returned to the camera, the switch63 is opened and then closed again to step the stepping relay toposition 6. Current passes through line 112 through the time-delay 113,and line 114 to the reverse relay 115. The contact 116 of the time-delay113 is normally open and does not close for a selective period of time.When the reverse relay 115 is activated, current flows through lines 75,117, reversing relay 80 and line 76 to energize the reversing relay 80and raise the contacts 81 and 83. In this position of the relay, currentflows from battery 77 through line 118, contact 83, line 82, motor 16,line 79, contact 81, line 84, shunt 85, and line 86 to the battery 77 torun the motor 16 in the reverse direction and move the crawler in areverse direction in the pipe.

While reverse movement is sometimes desirable, it is not normallydesirable in successively inspecting welds, and for this reason thetime-delay 113 is provided in the reverse circuit. Thus, if within theperiod allowed by the time-delay 113 which is normally open, the controlswitch 63 is opened and then again closed to step the stepping relay toposition 7, the reverse circuit will not be energized. If the circuit isleft at position 6 until the time-delay 113 is activated, then thecrawler will be moved in the reverse direction.

It should be noted that forward relay 73 and reverse relay 80 areinterlocked so that both relays cannot be simultaneously operated. Withthe stepping relay 65 in position 7, it will be appreciated that thenormal cycle of operation has been completed and the pipeline inspected,the source returned to the shield, and the crawler is inactive in thepipeline. If a 6-contact relay were used, the cycle could be repeated.In order to increase the life of the relay 65, a l2-contact relay isutilized and the cycle above explained is repeated through contacts 7through 12 in the exact manner herein above explained.

From the above it is apparent that in the event of a power failure, theclutch 49 is de-energized and the spring 51 returns the source toretracted position if it is not already in this position.

FIG. 10 shows an alternate safety system that may be used if desired. Inthis system, instead of line 89 connecting directly to the source relay90 as shown in FIG. 8, connection to the source relay 90 is through line119 and the closed contact 120 of a time-delay indicated generally at121, and line 122. Current is provided to the time-delay 121 throughline 123 and line 124. The time-delay 121 would normally be for asubstantial time, say minutes, and a timing motor would be included.Thus, if the source is extended, the weld inspected and the sourcereturned to the shield within a normal period of time, the time-delay121 would remain closed and would not affect operation of the circuit.However, if through some malfunction the source remained in extendedposition due to the source extending circuit remaining activated, thenafter a selected period of time, the time-delay 121 would open contact120 to break the circuit to both the source relay 90 and the clutchrelay 93 to de-energize the source-extend circuit and energize thesource-return circuit.

From the above it will be seen that all of the objects of this inventionhave been attained. There has been provided a simple inexpensive controlsystem for controlling the movement of a crawler through a pipe and forcontrolling the exposure of radio-active source to inspect a weld. Itwill be appreciated that if an X-ray tube were used that control of theX-ray tube would be carried out in the manner taught by this invention.

While the operator has positive control of the source, suitablesafeguards are present which will insure that the source not remainextended through malfunction of the equipment.

The use of the shield narrows the direction of the high intensity raysto a 360 are which will pass through the circumferential weld of thepipe. As the lead camera is in line with the tube 33 a complete shieldin both directions along the pipe is provided. This will protect peoplealong the pipeline in either direction and greatly simplify protectionof personnel as it is only necessary to insure that personnel are notpresent in a direction perpendicular to the pipeline in the area of theweld.

While a simple stepping coil and relays are employed in the systemshown, it will be appreciated that more sophisticated electronicstepping systems might be employed if desired.

The foregoing disclosure and description of the invention areillustrative and explanatory thereof and various changes in the size,shape and materials, as well as in the details of the illustratedconstruction, may be made within the scope of the appended claimswithout departing from the spirit of the invention.

What is claimed is:

1. A crawler comprising,

a body,

means on the body including a motor for moving the crawler through apipeline,

a source of rays carried by the body for exposing film,

control means for said motor and said source including a signalreceiver,

and sending means for selectively generating a magnetic signalincludingan electromagnetic means positionable on the exterior of and adjacentthe pipeline and generating signals from outside of the pipeline atselected positions therealong,

said sending means and said signal receiver being so related that theymust be in close proximity to each other before the control meansresponds to the sending means, whereby the crawler may be stopped in thepipeline at a selected position by locating the sending means at saidposition,

said control means responsive to successive electromagnetic signals fromoutside the pipeline to stop the crawler, pass through a pipeline toinspect a weld, shut off said rays, and restart the crawler.

2. A crawler comprising,

a body,

means on the body including a motor for moving the crawler through apipeline,

a shield carried by the body,

a source of radio-active material movable between a position inside ofand a position outside of the shield,

control means for starting and stopping said motor and for moving saidsource between said positions,

said control means including a signal receiver,

and magnetic signal generating means including sending meanspositionable on the exterior of and adjacent the pipeline and generatingsignals from outside of the pipeline at selected positions therealong,

said signal generating means and said signal receiver being so relatedthat they must be in close proximity to each other before the controlmeans responds to the signal generating means, whereby the crawler maybe stopped in the pipeline at a selected position by locating thesending means at said position,

said control means being responsive to successive electromagneticsignals from outside the pipeline to stop the crawler, pass rays througha pipeline to inspect a weld, shut off said rays and restart thecrawler,

and safety means for moving said source into said shield in the absenceof a retract signal from said signal generator a selected time after thesource is moved out of the shield.

3. The crawler of claim 2 wherein safety means includes a time delaymeans which releases all restraints on movement of the source andresilient means moves the source into the camera shield.

4. A crawler comprising, a body,

means on the body including a motor for moving the crawler through apipeline,

a shield carried by the body,

a source of radio-active material,

means for moving the source between a position inside of and a positionoutside of the shield,

magnetic signal-generating means including sending means positionable onthe exterior of and adjacent the pipeline and generating signals fromoutside of the pipeline at selected positions therealong, and controlmeans for starting and stopping said motor and for moving said sourcebetween said positions comprising,

a signal receiver positioned to be adjacent the wall of a pipeline inwhich the crawler is contained to receive electro-magnetic signals fromoutside the pipeline, stepping means movable one position each time itreceives a signal from said signal receiver with alternate positionsbeing operative and inoperative, means responsive to the stepping meansmoving to its first position for starting said motor and responsive tothe stepping means moving to its second position for stopping saidmotor, and means responsive to the stepping means moving to its thirdposition for moving the source out of the shield and responsive to thestepping means moving to its fourth position for moving the source intothe shield. 5. The crawler of claim 4 wherein if the source is not inthe shield a selected time after the stepping means moves to its fourthposition a time delay means releases all restraints on movement of thesource and resilient means moves the source into the shield.

6. The crawler of claim 4 wherein means are provided for moving saidsource into said shield in the absence of a retract signal from saidsignal generator a selected time after the source is moved out of theshield.

7. The crawler of claim 4 wherein means are provided responsive to thestepping means moving to its fifth position for reversing the motor andfor stopping the motor responsive to the stepping means moving to itssixth position.

8. The crawler of claim 7 wherein a time delay is provided in thereversing means whereby the motor will not reverse if the stop signal isreceived within the time delay.

9. A crawler comprising,

a body,

means on the body including a motor for moving the crawler through apipeline,

a shield carried by the body,

a source of radioactive material, movable between a position inside ofand a position outside of the shield,

means for moving said source between said positions including areversing motor connected to the source through a clutch,

resilient means for returning said source to the shield when the clutchis operated to disconnect the motor from the source, signal generatingmeans in-- cluding an electro-magnet positionable on the exterior of apipeline and generating signals from outside of the pipeline at selectedpositions therealong,

and control means for operating said motor and clutch comprising, asignal receiver positioned to be adjacent the wall of a,pipeline onwhich the electro-magnet is positioned to receive electro-magnetlcsignals from outside the pipeline,

stepping means movable one position each time it receives a signal fromsaid signal receiver with alternate positions being operative andinoperative,

means responsive to the stepping means moving to its first position forstarting the crawler motor and responsive to the stepping means movingto its second position for stopping said motor,

and means responsive to the stepping means moving to its third positionfor moving the source out of the shield and responsive to the steppingmeans moving to its fourth position for moving the source into theshield including time delay means operative to disengage the clutch andrelease the source motor from the source if the source does not returnto the shield within a selected time after the stepping means is movedto the fourth position.

10. The crawler of claim 9 wherein means are provided for moving thesource into the shield in the absence of a signal from said signalgenerator a selected time after the source is moved out of the shield.

11. The crawler of claim 9 wherein means are provided responsive to thestepping means moving to its fifth position for reversing the crawlermotor and for stopping the motor responsive to the stepping means movingto its sixth position.

12. The crawler of claim 11 wherein a time delay is provided in thereversing means whereby the motor will not reverse if the stop signal isreceived within the time delay.

13. The crawler of claim 9 wherein the clutch is electric and releasesthe source motor from the source in the absence of electric power.

1. A crawler comprising, a body, means on the body including a motor formoving the crawler through a pipeline, a source of rays carried by thebody for exposing film, control means for said motor and said sourceincluding a signal receiver, and sending means for selectivelygenerating a magnetic signal including an electro-magnetic meanspositionable on the exterior of and adjacent the pipeline and generatingsignals from outside of the pipeline at selected positions therealong,said sending means and said signal receiver being so related that theymust be in close proximity to each other before the control meansresponds to the sending means, whereby the crawler may be stopped in thepipeline at a selected position by locating the sending means at saidposition, said control means responsive to successive electro-magneticsignals from outside the pipeline to stop the crawler, pass through apipeline to inspect a weld, shut off said rays, and restart the crawler.2. A crawler comprising, a body, means on the body including a motor formoving the crawler through a pipeline, a shield carried by the body, asource of radio-active material movable between a position inside of anda position outside of the shield, control means for starting andstopping said motor and for moving said source between said positions,said control means including a signal receiver, and magnetic signalgenerating means including sending means positionable on the exterior ofand adjacent the pipeline and generating signals from outside of thepipeline at selected positions therealong, said signal generating meansand said signal receiver being so related that they must be in closeproximity to each other before the control means responds to the signalgenerating means, whereby the crawler may be stopped in the pipeline ata selected position by locating the sending means at said position, saidcontrol means being responsive to successive electro-magnetic signalsfrom outside the pipeline to stop the crawler, pass rays through apipeline to inspect a weld, shut off said rays and restart the crawler,and safety means for moving said source into said shield in the absenceof a retract signal from said signal generator a selected time after thesource is moved out of the shield.
 3. The crawler of claim 2 whereinsafety means includes a time delay means which releases all restraintson movement of the source and resilient means moves the source into thecamera shield.
 4. A crawler comprising, a body, means on the bodyincluding a motor for moving the crawler through a pipeline, a shieldcarried by the body, a source of radio-active material, means for movingthe source between a position inside of and a position outside of theshield, magnetic signal-generating means including sending meanspositionable on the exterior of and adjacent the pipeline and generatingsignals from outside of the pipeline at selected positions therealong,and control means for starting and stopping said motor and for movingsaid source between said positions comprising, a signal receiverpositioned to be adjacent the wall of a pipeline in which the crawler iscontained to receive electro-magnetic signals from outside the pipeline,stepping means movable one position each time it receives a signal fromsaid signal receiver with alternate positions being operative Andinoperative, means responsive to the stepping means moving to its firstposition for starting said motor and responsive to the stepping meansmoving to its second position for stopping said motor, and meansresponsive to the stepping means moving to its third position for movingthe source out of the shield and responsive to the stepping means movingto its fourth position for moving the source into the shield.
 5. Thecrawler of claim 4 wherein if the source is not in the shield a selectedtime after the stepping means moves to its fourth position a time delaymeans releases all restraints on movement of the source and resilientmeans moves the source into the shield.
 6. The crawler of claim 4wherein means are provided for moving said source into said shield inthe absence of a retract signal from said signal generator a selectedtime after the source is moved out of the shield.
 7. The crawler ofclaim 4 wherein means are provided responsive to the stepping meansmoving to its fifth position for reversing the motor and for stoppingthe motor responsive to the stepping means moving to its sixth position.8. The crawler of claim 7 wherein a time delay is provided in thereversing means whereby the motor will not reverse if the stop signal isreceived within the time delay.
 9. A crawler comprising, a body, meanson the body including a motor for moving the crawler through a pipeline,a shield carried by the body, a source of radio-active material, movablebetween a position inside of and a position outside of the shield, meansfor moving said source between said positions including a reversingmotor connected to the source through a clutch, resilient means forreturning said source to the shield when the clutch is operated todisconnect the motor from the source, signal generating means includingan electro-magnet positionable on the exterior of a pipeline andgenerating signals from outside of the pipeline at selected positionstherealong, and control means for operating said motor and clutchcomprising, a signal receiver positioned to be adjacent the wall of apipeline on which the electro-magnet is positioned to receiveelectro-magnetic signals from outside the pipeline, stepping meansmovable one position each time it receives a signal from said signalreceiver with alternate positions being operative and inoperative, meansresponsive to the stepping means moving to its first position forstarting the crawler motor and responsive to the stepping means movingto its second position for stopping said motor, and means responsive tothe stepping means moving to its third position for moving the sourceout of the shield and responsive to the stepping means moving to itsfourth position for moving the source into the shield including timedelay means operative to disengage the clutch and release the sourcemotor from the source if the source does not return to the shield withina selected time after the stepping means is moved to the fourthposition.
 10. The crawler of claim 9 wherein means are provided formoving the source into the shield in the absence of a signal from saidsignal generator a selected time after the source is moved out of theshield.
 11. The crawler of claim 9 wherein means are provided responsiveto the stepping means moving to its fifth position for reversing thecrawler motor and for stopping the motor responsive to the steppingmeans moving to its sixth position.
 12. The crawler of claim 11 whereina time delay is provided in the reversing means whereby the motor willnot reverse if the stop signal is received within the time delay. 13.The crawler of claim 9 wherein the clutch is electric and releases thesource motor from the source in the absence of electric power.